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Effects of intravoxel velocity distributions on the accuracy of the phase-mapping method in phase-contrast MR angiography

✍ Scribed by Craig A. Hamilton; Paul R. Moran; Peter Santago; II; Sarah A. Rajala

Publisher
John Wiley and Sons
Year
1994
Tongue
English
Weight
426 KB
Volume
4
Category
Article
ISSN
1053-1807

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✦ Synopsis

Abstract

The phase‐mapping method of phase‐contrast magnetic resonance angiography is shown to be based on an implicit assumption that the intravoxel velocity distribution is symmetric about its mean velocity. The effect of asymmetric distributions on the accuracy of quantitative average velocity measurements is determined analytically and verified experimentally. An explicit formulation is developed for the estimated average velocity in a voxel as a function of the true average velocity and the asymmetry of the distribution about the true average velocity. Worst‐case distributions are determined for unidirectional and bidirectional flow, and the special case of laminar flow is also investigated. Computer simulations and phantom imaging experiments demonstrate the accuracy of the analysis. For voxels with unidirectional flow, the phase‐mapping method produces accurate estimates of average velocity, while results for bidirectional flow indicate possible large errors unless the aliasing velocity is increased. which decreases the signal‐to‐noise ratio in the resultant velocity map image.

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